A radio relay apparatus, also referred to as a “repeater” or “booster,” receives and amplifies signals transmitted from a base station apparatus and transmits the signals into the coverage area, and also receives and amplifies signals transmitted from a communication terminal apparatus located in the coverage area and transmits the signals to the base station apparatus, in order to make a radio wave dead zone a radio communicable area.
Furthermore, a mobile communication relay apparatus disclosed in Patent Document 1 is known as an apparatus to make a radio wave dead zone a communicable area. In slave unit side 1According to Patent Document 1, antenna modules 6-1, 6-2, . . . , 6-n provided in respective slave units are cascaded via input/output terminal 2, wiring coaxial cables 3-0, 3-1, . . . , 3-(n−1) and high-frequency couplers 4-1, 4-2, . . . , 4-n.
In such a mobile communication relay apparatus, when a plurality of slave units (i.e. antenna modules) are cascaded to slave unit side 1A, downlink transmission power outputted from the slave units is preferably set uniform between all slave units. Therefore, the degree of coupling Ci of high-frequency couplers 4-1, 4-2, . . . , 4-n with each slave unit is set with unique values, depending on the routing lengths and so on of wiring coaxial cables 3-0, 3-1, 3-2, . . . , 3-(n−1), 15-1, 15-2, . . . , 15-n. When downlink transmission power is distributed to each slave unit in this way, the power transmitted from antenna 10 depends only upon the deviation of the lengths of wiring coaxial cables 15-1 to 15-n, and therefore transmission power can be supplied to all slave units, at substantially the same level, without causing any problem by taking into account only the wiring lengths of coaxial cables upon distributing slave units.
Furthermore, the mobile communication relay apparatus shown in FIG. 6 of Patent Document 1 is further provided with BPF 9 and amplifier 12 having a variable gain function right below a downlink antenna, so as to control the output power of amplifier 12 autonomously by a detection signal of detection circuit 12a. In this way, the deviation of downlink transmission power, which depends upon the lengths of the coaxial cables, can be improved by adjusting the amplifier gains of the individual slave units.
Patent Document 1: Japanese Patent Application Laid-Open No. 2004-215191